In recent years, there has been increasing interest in metal halide lamps, i.e., electric discharge devices which emit color-modified light and contain various metal halides as additives. The useful life of these lamps may range from 6,000 to over 10,000 hours, and the efficiency, measured in lumens of light per watt, of metal halide lamps in many instances is greater than 100.
In the preparation of these lamps, additive metal halides have been pulverized or powdered, and then pelleted in a desired mass or weight for machine feeding to the arc tube or envelope of the lamp. These metal halides, however, have contained impurities such as water and various hydroxides. Flaming, i.e., heating with a hand torch, has been used to drive off the water, but this procedure does not normally remove the hydroxide impurities, and has a further disadvantage in that other volatile material, desirably left in the lamp, is also driven off with the water.
The presence of hydrogen and oxygen in any form within the lamp envelope is detrimental to the lamp. These detriments may exist not only as free hydrogen and oxygen, but also as compounds thereof such as water, hydroxides, sulfates and silicates. The oxygen present within the envelope of the lamp oxidizes the metals such as tungsten which make up the lamp electrodes or filaments, and the resulting metal oxide condenses upon the interior surface of the lamp envelope thereby reducing lamp efficiency. The hydrogen present within the envelope of the lamp then reduces the oxide back to the metal freeing the oxygen to further corrode and remove more of the metal from the filament or electrode and further clouding the envelope by depositing the metal on the interior surface thereof. Thus, the lamp envelope becomes increasingly cloudy with a corresponding reduction in the efficiency of the lamp, and the metal filaments are deteriorated reducing the useful life of the lamps.
Accordingly, a primary object of the present invention is to provide novel apparatus for producing ultra-pure metal halide particles of controlled size.
Other objects and advantages of the present invention will become apparent from the following.
In accordance with one aspect of the present invention, apparatus is provided for producing discrete particles of purified metal halide, which apparatus comprises vessel means for holding molten halide, means for passing a gas through the interior of the vessel means, conduit means in communication with the vessel means, means for heating the vessel means and the conduit means, a quenching chamber disposed outwardly from the conduit means whereby molten halide passing from the vessel means through the conduit means discharges into the quenching chamber, and means for vibrating the conduit means whereby molten halide discharges from the conduit means in a continuous stream and separates in the quenching chamber into droplet form.
In a preferred embodiment, the apparatus further comprises filter means disposed between the vessel means and the conduit means, the interior diameter of the nozzle or discharge end of the conduit means is from about one-half to about one-sixth, and advantageously about one-third to about one-fifth, of the average diameter of the quenched particles produced, and the vibrating means comprises a member having one end disposed in mechanical energy transferring relation to the nozzle or discharge end of the conduit and the other end in energy transferring relation with an electro-mechanical transducer.
These and other aspects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from the claims and following more detailed description of a preferred embodiment when read in conjunction with the appended drawings.